Mass flow measuring or controlling device

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of German Patent Application No. 20 2011 109 511.1 filed on Dec. 23, 2011 and German Patent Application No. 20 2012 001 121.9 filed on Feb. 6, 2012 in the German Patent and Trade Mark Office (DPMA), the disclosure of which is incorporated herein in their entirety by reference.

TECHNICAL FIELD

The invention relates to a mass flow measuring or controlling device.

BACKGROUND OF THE INVENTION

Mass flow measuring or controlling devices are for example known from document DE 10 2004 019 521 A1 and are intended to reliably measure or control flow rates of gases or liquids with high precision also over a relatively large flow range.

Mass flow measuring or controlling devices which are based on a thermal measuring principle usually comprise a sensor element which is arranged on a sensor support part and adjoins a flow channel.

There are two basic variants of mass flow measuring or controlling devices of this type with respect to the flow channel. The design mostly used so far provides that a main flow channel is provided in the housing, from which a bypass channel is branched off. The sensor element measures at the bypass channel. In the region of the main flow channel, which in terms of flow is parallel to the bypass channel, a flow resistance section is present to generate a drop in pressure. The design of the mass flow measuring or controlling device alternative thereto does not provide any bypass channel. Rather, the entire fluid flow will flow past the sensor element.

In the embodiment having a bypass channel, the latter requires a certain minimum length which is due to the fact that it is arranged above a flow divider generating a drop in pressure, so that only part of the entire flow flows through the bypass channel. Furthermore, flow conditions which are as constant as possible are to be achieved in a measuring section arranged in the bypass channel.

For a constant measuring accuracy, it is decisive that the spatial arrangement between the sensor element and the measuring section in the flow channel remains unchanged over the service life of the mass flow measuring or controlling device.

In particular in case of low flow rates, for example at 100 ml/min up to 1 ml/min, it is difficult to achieve a high control accuracy of 1-2%, for example. A pressure dependence of the control accuracy having a particularly high impact in this region is determined. A pressure loading on the parts contacted by the medium in the device can undesirably lead to the fact that the sensor support part slightly moves away from the flow channel in the region of the sensor element by a bending of the sensor support part, which results in a degradation of the control accuracy.

It is therefore the object of the invention to provide a mass flow measuring or controlling device which does not include the drawbacks mentioned above, which is stable under compressive loading and which has a high control accuracy, also in the range of very low flow rates of up to 1 ml/min.

SUMMARY OF THE INVENTION

The mass flow measuring or controlling device according to the invention has a base body, a flow channel and a sensor module which comprises a sensor element and which can be coupled to an electronic unit. The flow channel has a measuring channel section which is in fluidic contact with the sensor element. The sensor element comprises a sensor support part which is in particular cuboidal, and a stabilizing element for stabilizing the sensor support part in the region of the measuring channel section.

To bring the sensor element in fluidic contact with the flow channel, the sensor support part has to be mounted to the mass flow measuring or controlling device. To this end, fastening means, such as screws, are often used. The fastening means are to be arranged outside the flow channel to prevent the flow of the medium in the flow channel from being unfavorably influenced. Furthermore, a medium contact with the fastening means is to be avoided for durability and contamination reasons.

Due to the design or the geometry, regions of the sensor support part which directly adjoin the fastening means can be exposed to a higher compressive loading than regions which are arranged at a larger distance from the fastening means. As the fastening means are for example arranged outside the flow channel, especially the region of the sensor support part in which the sensor element is located is less resistant to a compressive loading. This drawback counteracts the stabilizing element.

The stabilizing element may provide that the sensor support part still withstands high pressures in the region of the measuring channel section which is in fluidic contact with the sensor element and does not directly adjoin the fastening means. This means that the fluidic contact between the measuring channel section and the sensor element is always ensured under compressive load and that the sensor support part does not undesirably slightly move away from the adjacent flow channel, for example by a bending in the region of the sensor element. The measuring accuracy is thus improved.

The measuring channel section may be arranged outside the base body, i.e. the flow runs first in the base body to be then guided out thereof. This variant has the advantage that the sensor module is placed from the outside onto the base body and that only branch canals of the flow channel within the body are to be guided from the base body to the outside. A replacement of the sensor module is also very simple in this variant. It must however be pointed out that it would of course also be possible to completely open the base body in the region of the measuring channel section and to close it again on an open side using the sensor module.

The flow channel present within the base body is referred to as main flow channel. In case no bypass is provided, it is possible to guide the flow from this main flow channel outwards to the sensor module and then back again into the base body. Alternatively, the main flow channel completely extends through the base body, and a bypass channel to the main flow channel forms the so-called measuring channel section along a section.

It is rather possible to dispense with the bypass in case of low mass flows than in case of high mass flows.

To simplify the manufacture of the base body with the main flow channel, a kind of modular system is provided. Depending on whether the mass flow measuring or controlling device is designed for large or small mass flows, an insert placed in the main flow channel is configured as a separation or as a throttling point. In case the insert is intended to cause a flow separation, two separate sections are formed in the main flow channel, which are brought in flow communication by a connecting channel. A section of the connecting channel is then the measuring channel section.

The sensor support part and/or the stabilizing element can be configured so as to be plate-shaped, in particular cuboidal. Plate-shaped parts are favorable in view of their manufacture and handling. Furthermore, they can be sealed in a simple manner. It is favorable to adjust the geometry of the sensor support part and that of the stabilizing element to each other. The devices can thus in particular also be mounted in a space-saving manner.

The stabilizing element may have an arched shape and presses the sensor support part towards the base body by means of its bulged section, in particular in the region of the sensor element. The stability of the system is thus increased especially at that point at which the measured values are acquired, which directly improves the measuring accuracy.

Moreover, the arched shape of the stabilizing element has the advantage that a stabilizing force originating therefrom is introduced into the system in a very purposeful and directed manner. The stabilizing force has the strongest effect along the apex line of the arch.

The stabilizing element can be configured as a spring plate. A spring plate is particularly suitable to absorb possibly occurring pressure impulses. The spring force of the spring plate increases the tightness and counteracts a possible bending of the sensor support part due to the fluid pressure. Alternatively, it is of course also possible to use other spring elastic elements.

The stabilizing element has in particular substantially the same base as the sensor support part such that it completely covers the latter on one side.

The sensor support part and the stabilizing element are locked to the base body by fastening means. The sensor support part and the stabilizing element are thus spatially in proximity to the flow channel arranged in the base body. Short medium channels or ducts have a favorable effect on measurement dynamics.

The sensor support part and the stabilizing element can be detachably fastened to the base body so as to be stacked on top of each other, the stabilizing element stabilizing the sensor support part on the rear side.

The stabilizing element immediately contacts the sensor support part on the rear side of the support part, e.g. in the region of the sensor element.

The sensor support part, the stabilizing element, the electronic unit and the optional fluid channel plate are all plate-shaped and have substantially the same basic surface area.

A detachable fastening simplifies maintenance works of the mass flow measuring or controlling device possibly required or desired during customer use. If necessary, the sensor support part and/or the stabilizing element can also simply be replaced.

Screws or clips, for example, which cooperate with threads or grooves to be provided in the base body, are suitable as fastening means.

The measuring channel section is e.g. configured as a recess in an exterior surface of the base body adjacent to the sensor support part. As the main flow channel is realized in the base body from which the flow is guided to the measuring channel section, short fluidic connections between the main flow channel in the base body and the measuring channel section can be produced in this arrangement of the measuring channel section.

However, it is also possible that the measuring channel section is arranged as a recess in an exterior surface of a separate fluid channel plate, which is adjacent to the sensor support plate, the fluid channel plate being detachably fastened to the base body. This has the advantage that the modularity is increased, which means that the fluid channel plates may be configured in an application-specific manner and, if necessary, can simply be replaced.

The geometry of the fluid channel can be adapted to the properties of the medium. The measuring channel section can, for example, be configured as a smaller or larger recess in the fluid channel plate depending on the viscosity of the medium. Similarly, the material of which the fluid channel plate is manufactured may also be selected depending on the medium.

The measuring channel section can be closed by a side face of the adjacent sensor support part. In this way, the measuring channel section is configured as a contour within the fluid channel plate or the base body and can be sealed in a simple manner.

The sensor element has electrical contacts for the coupling to the electronic unit, so that the measured values acquired by the sensor element can be evaluated directly.

The electrical contacts can be guided through the sensor support part and the stabilizing element to an exterior surface facing away from the base body. This has the advantage that the electronic unit does not come into contact with the medium, as a result of which the service life of the electronic components is increased.

The electronic unit may be part of the device and is configured as a printed circuit board which is detachably fastened to the base body along with the sensor support part and the stabilizing element. The mass flow measuring or controlling device can therefore be manufactured as a compact unit.

An interface for transmitting data acquired by the sensor element is e.g. arranged on the printed circuit board. The interface can, for example, be configured as a bus interface via which measured data is transmitted to an evaluation unit. However, it is also possible to connect a display.

The sensor module, the electronic unit and the optional fluid channel plate can be stacked on top of each other and configured as a pre-mounted unit, which is favorable with respect to assembling and stocking.

The sensor module is detachably fastened, in particular screwed to the base body as a pre-mounted unit. The fastening can however also be realized using other known methods, by means of clips, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a perspective top view on a mass flow measuring or controlling device according to the invention in the pre-mounted state,

<figref idref="DRAWINGS">FIG. 2</figref> is a perspective top view on a mass flow measuring or controlling device according to the invention in the mounted state,

<figref idref="DRAWINGS">FIG. 3</figref> is a longitudinal sectional view of the mass flow measuring or controlling device according to the invention of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 4</figref> is a longitudinal sectional view of the mass flow measuring or controlling device according to the invention of <figref idref="DRAWINGS">FIG. 2</figref>;

<figref idref="DRAWINGS">FIG. 5</figref> is a longitudinal sectional view of the mass flow measuring or controlling device of the invention according to a further embodiment; and

<figref idref="DRAWINGS">FIG. 6</figref> is a longitudinal sectional view through a mass flow measuring or controlling device slightly modified with respect to the device of <figref idref="DRAWINGS">FIG. 5</figref>.

DETAILED DESCRIPTION

<figref idref="DRAWINGS">FIG. 1</figref> shows a perspective top view on a mass flow measuring or controlling device <b>10</b> according to the invention in a pre-mounted state, having in its interior at least one flow channel. A main flow channel <b>14</b> projects in the longitudinal direction through a substantially cuboidal base body <b>12</b>.

A fluid channel plate <b>16</b>, a sensor support part <b>18</b>, a stabilizing element <b>20</b> and an electronic unit <b>22</b> are arranged stacked on top of each other on a side face of the base body <b>12</b> which is e.g. parallel to the longitudinal direction, and are detachably connected to the base body <b>12</b> by fastening means <b>24</b>, for example screws. It is however also possible to use other fastening means, such as clips or brackets.

The screws are shown in <figref idref="DRAWINGS">FIG. 1</figref> to be not yet tightened up to an end position.

The fluid channel plate <b>16</b>, the sensor support part <b>18</b>, the stabilizing element <b>20</b> and the electronic unit <b>22</b> each have a cuboidal, in particular plate-shaped geometry. The plate-shaped geometry permits a very compact and space-saving design. It is however also possible to choose a different geometry.

The sensor support part <b>18</b> comprises a sensor element which is not shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref> and is described in detail in the descriptions of <figref idref="DRAWINGS">FIGS. 3 and 4</figref>.

Whereas the fluid channel plate <b>16</b>, the sensor support part <b>18</b> and the electronic unit <b>22</b> are configured in a flat manner on opposite exterior surfaces, the stabilizing element <b>20</b> has an arched shape having a bulged section <b>26</b> and two legs <b>28</b>. The bulged section <b>26</b> of the stabilizing element <b>20</b> rests against the sensor support part <b>18</b> in the region of the sensor element.

The two legs <b>28</b> are in particular bent through 2° with respect to the sensor support part <b>18</b> so as to be directed away therefrom.

The stabilizing element <b>20</b> has in particular a thickness of 2 mm.

The stabilizing element <b>20</b> is e.g. configured as a spring element and made of a spring steel. However, other stabilizing elements <b>20</b> are also conceivable which press onto the sensor support part <b>18</b> in the region of the sensor element.

The electronic unit <b>22</b> has an interface <b>30</b> for transmitting measured values acquired by the sensor element. The interface <b>30</b> is e.g. configured as an internal bus interface for the communication with an evaluation or regulation unit (not represented). The data can however also be transmitted in other known data transmission ways to the evaluation or regulation unit, for example electrically, inductively, by radio or in a wireless manner. The interface <b>30</b> is configured correspondingly depending on the desired data transmission way.

In contrast to <figref idref="DRAWINGS">FIG. 1</figref>, <figref idref="DRAWINGS">FIG. 2</figref> shows the fastening means <b>24</b> in the mounted state in their end position, the legs <b>28</b> of the stabilizing element <b>20</b> being pressed towards the sensor support part <b>18</b> such that the sensor support part <b>18</b> and the stabilizing element <b>20</b> take positions that are substantially parallel to each other. The stabilizing element <b>20</b> presses onto the sensor support part <b>18</b> in the region of the sensor element <b>40</b> and stabilizes the latter on the rear side, as a result of which the sensor support part <b>18</b> remains dimensionally stable also in case of a high compressive loading.

<figref idref="DRAWINGS">FIG. 3</figref> shows the mass flow measuring or controlling device <b>10</b> of <figref idref="DRAWINGS">FIG. 1</figref> in the pre-mounted state.

The base body <b>12</b> is also passed through by the main flow channel <b>14</b>. The fluid channel plate <b>16</b>, the sensor support part <b>18</b>, the stabilizing element <b>20</b> and the electronic unit <b>22</b> are arranged stacked on top of each other on a side face of the base body <b>12</b> and are detachably connected to the base body <b>12</b> by fastening means <b>24</b>, as already represented in <figref idref="DRAWINGS">FIG. 1</figref>.

Sensor support part <b>18</b>, stabilizing element <b>20</b>, electronic unit <b>22</b> and fluid channel plate <b>16</b> are all plate-shaped and have substantially the same basic surface area and may have different thicknesses.

A flow conditioning insert <b>32</b> having a flow resistance element <b>34</b> is arranged axially in the main flow channel <b>14</b>. A bypass channel <b>36</b> parallel to the main flow channel and having two connecting channels <b>38</b> is branched off from the main flow channel <b>14</b> and guided back such that the flow resistance element <b>34</b> is arranged between the two connecting channels <b>38</b> to generate a pressure difference.

The flow channel in the device <b>10</b> comprises the main flow channel <b>14</b> and the bypass channel <b>36</b> along with the connecting channels <b>38</b>.

The bypass channel <b>36</b> extends laterally to the outside of the base body <b>12</b> into the fluid channel plate <b>16</b>.

The bypass channel <b>36</b> is configured there as a recess in the fluid channel plate <b>16</b> open upwards, which is arranged on a side face of the base body <b>12</b>. The fluid channel plate <b>16</b> is optional, as the bypass channel <b>36</b> can alternatively also be configured as a recess <b>50</b> on the side face of the base body <b>12</b> (see broken line in <figref idref="DRAWINGS">FIG. 3</figref>). The connecting channels <b>38</b> open into the fluid channel plate <b>16</b> and merge into the bypass channel <b>36</b>.

The bypass channel <b>36</b> is closed by an adjacent side face of the sensor support part <b>18</b> on which the sensor element <b>40</b> is arranged.

The sensor element <b>40</b> is in fluidic contact with the bypass channel <b>36</b> in the region of a measuring channel section <b>42</b>, this region being stabilized on the rear side by the stabilizing element <b>20</b>.

The sensor element <b>40</b> has electrical contacts <b>44</b> which are guided through the sensor support part <b>18</b> and the stabilizing element <b>20</b> to an exterior surface facing away from the base body <b>12</b>. The electrical contacts <b>44</b> open into the interface <b>30</b> which is arranged onto the electronic unit <b>22</b>.

The electronic unit <b>22</b> is e.g. configured as a printed circuit board and, as described above, is detachably fastened to the base body <b>12</b> along with the optional fluid channel plate <b>16</b>, the sensor support part <b>18</b> and the stabilizing element <b>20</b> by fastening means <b>24</b>.

The optional fluid channel plate <b>16</b>, the sensor support part <b>18</b>, the stabilizing element <b>20</b> and the electronic unit <b>22</b> are e.g. assembled as a pre-mounted unit which is detachably fastened to the base body <b>12</b>.

It is however also possible to first connect the sensor support part <b>18</b> to the stabilizing element <b>20</b> and to detachably mount it directly to the base body <b>12</b> in case the measuring channel section <b>42</b> is configured as a recess in a side face of the base body.

It is essential to the invention that the sensor support part <b>18</b> is stabilized by the stabilizing element <b>20</b> against the fluid pressure in the region of the measuring channel section <b>42</b>, so that it is ensured that the sensor element <b>40</b> is in constant fluidic communication with the measuring channel section <b>42</b> also under a compressive load by the medium, and the sensor support part <b>18</b> is not undesirably bent, so that the measurement accuracy is increased and almost pressure independent.

<figref idref="DRAWINGS">FIG. 4</figref> represents a front view of the mass flow measuring or controlling device <b>10</b> of the invention according to <figref idref="DRAWINGS">FIG. 2</figref>, also in the mounted state and in a half section.

In contrast to <figref idref="DRAWINGS">FIG. 3</figref>, the fastening means <b>24</b> are in their end position. The stabilizing element <b>20</b> rests substantially in a parallel manner on the sensor support part <b>18</b> and presses on the rear side against the sensor support part <b>18</b> in the region of the sensor element <b>40</b>, so that the fluidic contact between the sensor element <b>40</b> and the bypass channel <b>36</b> is reliably ensured in the region of the measuring channel section <b>42</b>.

The embodiment according to <figref idref="DRAWINGS">FIG. 5</figref> substantially corresponds to the embodiment shown in the previous figures, the reference numbers already introduced being used for the same or similar components. Only the differences are therefore described in detail in the following.

Whereas in the preceding embodiments a main flow channel <b>14</b> extending through the base body <b>12</b> is provided, the main flow channel <b>14</b> is separated in the embodiment according to <figref idref="DRAWINGS">FIG. 5</figref>. It results two sections <b>50</b>, <b>52</b> of the main flow channel <b>14</b>. The separation of these two sections <b>50</b>, <b>52</b> is for example realized by an insert <b>32</b>′ which is inserted in the main flow channel <b>14</b> and which has a partition wall <b>54</b> to fluidically separate the two sections <b>50</b>, <b>52</b>.

The flow channel of the mass flow measuring or controlling device <b>10</b> is here configured without a bypass. The two sections <b>50</b>, <b>52</b> are brought in flow communication with each other by means of a connecting channel. This connecting channel is composed of the connecting channels <b>38</b> already mentioned above and of the channel <b>36</b>′ present in the sensor module, of which one section is the measuring channel section <b>42</b>.

A stabilizing element <b>20</b> is of course also provided in this embodiment, in which the sensor module is configured identically to the preceding sensor modules. The stabilizing element <b>20</b> is represented in the compressed position, as in <figref idref="DRAWINGS">FIG. 4</figref>.

Instead of the insert <b>32</b>′ with which the connecting wall <b>54</b> is integrally formed, it is also possible to use an insert <b>32</b>″ according to <figref idref="DRAWINGS">FIG. 6</figref>. The insert <b>32</b>″ includes an inserted flowproof partition wall <b>54</b>′ instead of the flow resistance element <b>34</b> which is inserted as a separate end wall (see <figref idref="DRAWINGS">FIG. 4</figref>). The advantage of this embodiment is that it is also possible to create a modular system with respect to the inserts <b>32</b>, <b>32</b>″. Depending on whether a bypass channel is to be present or not, an insert <b>32</b> having a flow resistance element <b>34</b> or a partition wall <b>54</b>′ is used.

The discs <b>58</b> present in the insert <b>32</b> to <b>32</b>″ upstream of the so-called discharge opening <b>56</b> are filter discs and/resistance elements.

In the embodiment according to <figref idref="DRAWINGS">FIG. 6</figref>, as in those discussed above, the corresponding sensor module is placed from the outside onto the base body <b>12</b> and screwed thereto, the stabilizing element <b>20</b> being not yet completely flattened in the position shown in <figref idref="DRAWINGS">FIG. 6</figref>, which means that the fastening means <b>24</b> are then not entirely tightened.

As shown in the Figures, fluid channel plate <b>16</b>, plate-shaped sensor support part <b>18</b>, plate-shaped stabilizing element <b>20</b>, and plate-shaped electronic unit <b>22</b> extend parallel to the flow channel <b>14</b>, <b>50</b>, <b>52</b> in base body and parallel to measuring channel section <b>42</b>.